The present invention relates to a knitting machine with needle control device for the knitting of pattern stitches.
As known, in order to produce patterns on knitted fabrics with knitting machines, the needles of the machine which are intended to operate in the region of the patterns are selected and actuated so as to produce held stitches or so as not to form knitting at one or more feeds or drops of the machine alternately to the stitches with which the bottom and possibly internal regions of the pattern are produced.
For example, in circular knitting machines, which comprise a needle holder element constituted by a cylinder on the lateral surface whereof a plurality of grooves is defined, said grooves being parallel to its axis, each groove slidably accommodating a needle and, below said needle, a selector, each needle and each selector having at least one heel which protrudes radially from the needle cylinder to engage in paths defined by the skirt of the cams which embrace the needle cylinder, upstream of each machine feed according to the rotary motion imparted to the cam skirt with respect to the needle cylinder, there are selection devices constituted by levers which can be controllably actuated so as to interfere or not interfere with the heels of the selectors so as to move the overlying needles to engage, with their heel, within paths which are an alternative to other paths, thus selecting the needles which must take the thread supplied to said feed.
One or more cams are provided between the selection device and the machine feed, in the cam skirt, and define a path for the heel of the needles or for the heel of sub-needles interposed between the selectors and the needles, with a first rising portion and, subsequent thereto, a second rising portion which move the needle so as to protrude with its point upward from the needle cylinder by such an amount as to engage the thread supplied by the feed.
More particularly, the engagement of the needle or sub-needle with the first rising portion causes the needle to rise to a level which is sufficient to engage the thread, whereas the loop formed previously by said needle slides along the point of the needle, opening the tab thereof without disengaging therefrom. The engagement of the needle or sub-needle with the second rising portion causes a further lifting of the needle to such a level that the previously formed loop disengages from the tab of the needle and descends along the needle stem. A lowering cam is provided downstream of the feed in the cam skirt and engages the heel of the needle so as to lower it, moving its point, with the thread engaged thereto, inside the previously formed loop, thus forming a new loop and disengaging the needle from the previous loop.
In order to knit normal knitting stitches, the heel of the needles or sub-needles engages the lifting cam both along the first rising portion and along the second rising portion and engages the descending portion of the lowering cam.
In order to knit a held stitch, the heel of the needle or sub-needle is prevented from engaging the second rising portion of the lifting cam.
Finally, in order to prevent the forming of knitting, the heel of the needle or sub-needle is prevented from engaging the lifting cam.
In order to prevent the heel of the needle or sub-needle from engaging the lifting cam or its second rising portion, i.e. in order to exclude a needle from knitting or to produce a held stitch, in some kinds of machine the sub-needles are provided elastically flexible, so that by acting on their heel it is possible to sink said heel into the related groove of the needle cylinder. In this manner the heel passes on the side of the lifting cam which is directed toward the needle cylinder and does not engage the rising portion upstream of which it has been sunk.
At the end of the lifting cam, the elasticity of the sub-needle causes the extraction of the heel, which can engage other cams of the cam skirt. To provide exclusion from knitting, the heel of the sub-needle is sunk upstream of the lifting cam by means of a control cam, whereas in order to produce a held stitch the sinking is performed, again by means of an adapted control cam, between the first rising portion and the second rising portion of the lifting cam.
Some problems are observed in machines which use flexible sub-needles to provide these types of knitting.
Since the needle is lowered with the lowering cam acting directly on the needle, the heel of all the needles, even those which are excluded from knitting at the feed being considered or which have produced a held stitch, engages in fact against said cam, with the disadvantage of a deformation of the loop engaged by the point of the needle if said loop is smaller than those formed at the feed being considered.
The assembly constituted by needle, sub-needle and selector furthermore has a considerable length which entails a corresponding height of the needle cylinder. Even greater problems occur in the needle plate in circular machines with two needle holders, since problems of bulk arise especially in small-diameter machines for the execution of the grooves in the direction of the plate axis since the grooves which accommodate said assembly are arranged radially.
Other kinds of machine use needles which can oscillate in a plane which is parallel to the sides of the groove in which they are accommodated, so as to move their heel from a sunk position to an extracted position or vice versa, by providing, between the side of the needle which is opposite to the heel and the bottom of the groove, a spring which keeps the needle with its heel in an extracted position but allows, by yielding elastically, to push, by means of appropriate cams, the heel into a sunk position to prevent its engagement for example with the lifting cam in order to exclude the needle from knitting at one feed, or with the second rising portion of said lifting cam in order to produce a held stitch.
The possibility of sinking the heel of the needles can avoid the engagement of the needles with the lowering cam for those needles which are excluded from knitting at the feed being considered and therefore also solves the problem of the deformation of the loop previously engaged by the needle.
Nonetheless, during the descent of the needle, the engaged thread, particularly in the case of scarcely elastic threads, exerts an action which can cause the unwanted sinking of the heel of the needle, with consequent disengagement from the lowering cam and therefore with faults in knitting and with the possibility of damage or breakage of the needle.